Ring rolling mill

ABSTRACT

A ring rolling mill has a pair of radial rolls acting on a workpiece ring by engaging radially opposite peripheries thereof, and a pair of axial rolls, which are preferably truncated conical rolls, acting axially on the ring by engaging axially opposite end surfaces thereof. The two rolls of each pair are adjustable toward each other and at least one roll of each pair is driven by associated adjustable speed driving means. One driving means is adjustable to a preselected nominal peripheral speed of the roll driven thereby, and a control adjusts the other driving means to set the peripheral speed of the roll driven thereby in accordance with the peripheral speed of the roll driven by the one driving means. Sensors engageable with the ring detect power transmission, through the ring, between the two driving means, and a second control is operable, responsive to detection of such power transmission by the sensors, to restore the peripheral speeds of the driven rolls into accordance with each other.

United States Patent [191 Jeuken et al.

[ 1 July 23,1974

[ RING ROLLING MILL [75] Inventors: Josef Jeuken, Holzwickede; GustavVieregge, Dortmund-Wambel; Konrad Meyer, Dortmund-Wickede, all ofGermany [73] Assignee: Rheinstahl AG, Essen, Germany [22] Filed: May 7,1973 [21] Appl. No.: 357,779

[30] Foreign Application Priority Data l/1973 Wieting et al. 72/10Primary Examiner-Lowell A. Larson Attorney, Agent, or Firm-McGlew andTuttle [5 7 ABSTRACT A ring rolling mill has a pair of radial rollsacting on a workpiece ring by engaging radially opposite peripheriesthereof, and a pair of axial rolls, which are preferably truncatedconical rolls, acting axially on the ring by engaging axially oppositeend surfaces thereof. The two rolls of each pair are adjustable towardeach other and at least one roll of each pair is driven by associatedadjustable speed driving means. One driving means is adjustable to apreselected nominal peripheral speed of the roll driven thereby, and acontrol adjusts the other driving means to set the peripheral speed ofthe roll driven thereby in accordance with the peripheral speed of theroll driven by the one driving means. Sensors engageable with the ringdetect power transmission, through the ring, between the two drivingmeans, and a second control'is operable, responsive to detection of suchpower transmission by the sensors, to restore the peripheral speeds ofthe driven rolls into accordance with each other.

17 Claims, 6 Drawing Figures PATENTED 3.824.820

PATENIEUmzmau sum 2 or 5 FIGS PAIENIEDamzsmu SHEET R [If 5 RING ROLLINGMILL FIELD AND BACKGROUND OF THE INVENTION This invention relates to aring rolling mill including a pair of radial rolls acting on a workpiecering by engaging radially opposite peripheries of the ring and a pair ofaxial rolls, which are preferably truncated conical rolls, actingaxially on the ring by engaging axially opposite end surfaces thereof,with the rolls of each pair being adjustable toward each other and atleast one roll of each pair being driven.

Such four-roll ring rolling mills are used to roll out, by radialexpansion under a press or a hammer, ring blanks produced from ingots byupsetting and punching, to form rings of rectangular or profiledcrosssection. The radial expansion of the ring is effected by the radialroll pair, of which the so-called disc roll is driven and the so-calledmandrel, for exerting the radial rolling force, is displaceable relativeto the disc roll. The axial rolls, acting on the axially end faces ofthe ring, serve mostly to calibrate the ring in height, that is, in theaxial direction, and to eliminate the constriction of the ring end facesoccurring during the rolling process. If, in addition to this,.aconsiderable axial rolling of the ring is to be effected with a highrolling force, there occurs a rather difficult problem that the ringmust have, in both roll gaps, identical circumferential speeds,andconsequently, the actual speeds of the drives of both roll pairs mustbe matched within narrow tolerance limits. If this is not achieved, aloop formation, rendering the ring unserviceable, or other ringformations, are inevitable, or at least there occurs, at the rolls, inthe case of very form-stiff rings which are adjusted by centeringwheels, a slip resulting in considerable load on the roll drives.

An attempt has already been made to avoid, or keep within harmlesslimits, the roll slip with its disadvantageous consequences for therolling process and for the work result, by design and by control means.For this purpose, in consideration of the different circumferen tialspeeds on the inner and outer peripheries of the ring, conical axialrolls have been used, and the geometry of the axial rolls, theirdisplacement radially of the ring, and/or their drive speed have been soselected or controlled that, on the basis of the geometricrelationships, rolling with little or no slip during the rolling processwas to be expected. In this connection, attention is directed to WestGerman Pat. No. 1,188,544 and to German laid open for inspectionapplication No. 1,752,887.

However, such ring rolling mills have not been satisfactory in practiceeither. Due to the narrow matching tolerances between the roll speeds,because of the flexibility of the roll drives, the, influence of thedeformation of the ring on the latters circumferential speed and, inparticular, because of the load-dependent contract point displacementsin the roll gaps resulting from the respective geometric conditions,difficulties still occur in the known ring rolling mills. Thesedifficulties interfere with the desired progress of the rollingoperation in that, from one of the roll grooves, forces act on the ringand which strive to push it out of the normal position determined by theroll grooves and possibly by the centering wheels, that is, the centerof the ring in the longitudinal axis of the rolling mill. These forcesmust be absorbed by corresponding counter forces of the centering wheelsor of the other roll groove. As soon as the moment of these forcessubjects the ring to higher stress than the resistance moment of thering crosssection decreasing during the rolling operation, theincreasing lever arm and the strength of the ring material permit, thering is deformed, sometimes suddenly, to complete uselessness.

SUMMARY OF THE INVENTION The problem to which the present invention isdirected is that of designing a ring rolling mill of the above-mentionedtype so that, during the rolling, the rings do not leave theirmirror-symmetrical position relative to the longitudinal axis of thering rolling mill, and the danger of ring deformation ca be reliablyavoided even if the rings are not very stiff.

The invention is based upon the realization that, for a disturbance-freerolling operation, it is not sufficient to match the speeds of thedriven rolls mutually according to the geometric design of the rolls.Instead, it is necessary to effect, during the rolling operation, acorrection of the ratio of the roll drive speeds in a manner whichcorresponds to the conditions of force, friction and contact, varyingduring the rolling operation. The point of contact between the rolls andthe ring end faces depends on the respective rolling force, the geometryof the ring cross-section, the friction value, etc., and shifts, duringthe rolling operation, in accordance with variations of these factors.When rolling with profiled disc rolls, that is, when rolling flanges,contact point shifts result not only in the axial groove but also in theradial groove.

It is a concrete object of the invention, therefore, to provide, byautomatic correction of at least one roll drive speed-or bycorresponding displacement of the conical axial rolls relative to thering, that the circum ferential speeds of the driven rolls of both rollgrooves are adapted to each other so that no forces that would disturbthe roundness of the ring act on the ring.

In accordance with the invention, the problem is solved in that thedrive of one roll pair is adjustable to a selectable nominal speed, aguide control sets the circumferential speed of the other roll pair inaccordance with this nominal speed or in accordance with the actualspeed to be measured, and one or more sensors, which detect a powertransmission from one roll pair to the other roll pair, restore thecircumferential speeds of the ring at both roll pairs into coincidencethrough a control or regulating device.

The ring rolling mill embodying the invention may be designed in variousembodiments, in particular with respect to the form of the sensors andthe setting members for the regulating device.

When, for example, as a result of a variation of the radial rollingforce, a displacement of the contact point toward the outer peripheryoccurs in a flanged ring, the circumferential speed of the ring at theradial roll pair increases, while it remains unchanged at the axial rollpair. As a result, at constant drive speeds, the ring migrates out ofits position of symmetry on one side, and transmits a portion of thedrive power of the radial roll pair to the axial roll pair, the portiontransmitted depending on the respective conditions. To avoid this, theremay be provided, in a ring rolling mill embodying the invention, twosensors, in particular two feeler wheels bearing against the outercircumference of the ring, which detect the position of the twocircumferential points of the ring perendicular to the common axialplane of the two radial rolls. Lateral migration of the ring causesunsymmetrical deflections of the two sensors which, through a measuringtransformer, supply corresponding input signals to the regulatingdevice. As the two sensors pick up at the same time, directly orindirectly, the ring diameter and thus also its diameter increase duringrolling, the signals associated with the sensors can be usedadditionally for displacing the axial roll pair in accordance with thering diameter increase, preferably so that the cone tips always lie onthe central axis of the ring or in the close vicinity thereof. If thecentral axis of the ring is to remain stationary during rolling, thesensors can further effect a displacement of the radial roll paircorresponding to the increase in the ring size.

Ring rolling mills often are provided with two centering wheels whichare arranged in mirror-symmetrical relation to the plane defined by theaxes of the two radial rolls, and which bear against the outercircumference of the ring. In accordance with the invention, one or bothcentering wheels may be designed as sensors, preferably so that thecentering wheels pick up the displacing force of the ring exerted on thecentering wheels. This can be attained, for example,'by providing acentering wheel suspension which is rotatable about a pivot axisarranged normal to the centering wheel axis and counter to the action ofa spring member, and that the displacement of the member is an inputquantity for a measuring transformer of the regulating device.

The centering wheels bear against the outer circumference of the ring,so that the displacing force of the ring, as its diameter increases,loads the spring members of both centering wheels uniformly. Lateralmigration of the ring causes opposite load variations of the springmembers, so that either by absolute measurement or by relativemeasurement a control signal is available for the regulating device.

Instead of the mentioned steady regulation by means of measuringtransformers, an unsteady regulation may be provided in that each of thetwo centering wheels, designed as a sensor, acts on a respective singlesetting member, so that, upon unsymmetrical actuation due to the ringposition having become unsymmetrical, the setting members effect,through a control device, either a corresponding variation of the speedof one driven roll or a displacement of the conical axial rolls relativeto the ring.

In a ring rolling mill embodying the invention, alternatively only onecentering wheel may be provided, preferably on that side of the ringrolling mill from which the ring enters the radial roll pair, becausethe drive and friction forces transmitted to the ring by the radialrolls exert a moment which strives to pivot the ring toward this side.

A ring rolling mill embodying the invention, in fact, makes possible soexact a matching as to identical circumferential speeds of the ring atboth roll pairs that additional centering of the ring with two centeringwheels, and possibly high bearing pressure, may not be necessary.

Different circumferential speeds of the ring at the two roll pairs, forexample, because of insufficient matching of the roll speeds, causes, inparticular in the case of stiffer rings, a transmission of drive powerfrom one roll pair to the other. In accordance with the invention, thiscan be avoided when the drive motor of each of the two roll pairs hasassociated therewith a measuring device which picks up the electricaleffective power used by the motors. By comparison of the output signalsof both measuring devices, a control signal can be obtained andexpresses deviations from the nominal value, for example, of thenumerical ratio of the two drive powers, and can annul undesired,non-static processes.

In the ring rolling mill, there may be arranged also, on at least one ofthe two roll pairs, a measuring device for picking up the effectiveelectric power of the drive motor and another measuring device forpicking up the rolling force. By comparison of the output signals of thetwo measuring devices, there is again available a control signal which,upon a deviation from the nominal value, indicates an undesired state ofthe rolling operation, and which consequently can be used for acorresponding correction of the factors involved. In ring rolling mills,it is desirable to transfer as high as possible a share of the drivepower into shaping power acting on the ring. If the particular ratiobetween drive power and rolling force is disturbed, for example, due tocontact point displacement in the roll gap because of lateral migrationof the ring and power transmissionv from one roll drive to the other,then this disturbing quantity is picked up by the control. The necessarycorrection of the selectable factors for the state of the rolling millcan be effected in various ways. In one embodiment of the invention, theregulating device comprises a setting member whose value influences thespeed of the drive of one roll pair. For this purpose, the regulator maybe designed so that its output signal is supplied as a correction factorto that part of the apparatus with which the basic matching of thespeeds of the two roll pairs is selectably set and automatically variedas the rolling operation progresses.

Alternatively, the regulating device may comprise a setting member whicheffects a displacement of the axial roll pair relative to the ring. Inthis case also, the regulator is advantageously designed so that itsoutput factor serves as a correction signal for that apparatus partwhich controls the shift drive of the axial roll pair when the latter isshifted outwardly following the increasing ring diameter.

The regulating device also may comprise one or two setting members whichinfluencethe rolling force exerted on the ring by one or both rollpairs. Such a regulated variation of the rolling force makes it possibleto annul or to render harmless an undesired contact point displacementwhich would cause a lateral migration of the ring and power transmissionbetween the two drives.

An object of the invention is to provide an improved ring rolling mill.

Another object of the invention is to provide such a ring rolling millin which, during rolling, the rings do not leave theirmirror-symmetrical position relative to the longitudinal axis of thering rollng mill.

A further object of the invention is to provide such a ring rolling millin which the danger of ring deformation can be avoided reliably even ifthe rings are not very stiff.

For an understanding of the principles of the invention, reference ismade to the following description of typical embodiments thereof asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 somewhat diagrammatically illustrates, in principle, theconstruction of a ring rolling mill embodying the invention, and inwhich the speed of the axial rolls is regulated;

FIGS. 2 and 3 are part sectional and part elevational views illustratingdetails of the centering wheels in a modified embodiment;

FIG. 4 is a view similar to FIG. 1 illustrating regulated displacementof the axial roll pair;

FIG. 5 is a side elevation view illustrating the mechanical constructionof a ringrolling mill embodying the invention, with the control meansomitted; and

FIG. 6 is a top plan view corresponding to FIG. 5."

Referring first to FIG. 1, the ring rollingmillshown therein comprises apair of radial rolls consisting of a disc roll 1 and a mandrel '2 whichis adjustable relative to disc roll 1. Opposite the pair of radialrolls, there is a pair of axial rolls consisting of two rolls 3 oftruncated cone form, ofwhich the lower conical rollis driven while theupper conical roll, which has not been shown, runs along and isadjustable relative to. the lower roll. In order that, with disc roll 1held fixedin the rollstand, the cone tips 4 of conical rolls 3 canbemaintained always on the center axis of the ring as the diameter of thering increases, and so that thus also ringscanbe rolled out whose finalradius is greater than the generatrix of conical rolls 3, the pair ofconical rolls is mounted to be horizontally displaceable in the rollstand. This has not been specificallyshown in FIG. 1. Alternatively, forsufficiently long cones, conical rolls 3 may be arranged fixed in therollstandand radial roll pair 1, 2 may be displaceable outwardly in theroll stand as the ring diameter increases.

The rolling mill has two centering wheels6 rotatable on pivot arms 7arranged mirror-symmetrically to the common axial plane of radialro1ls1'and -2, and which are pressed against the outer periphery of ring5 so that, upon increase of the ring diameter, wheels'6 are movedoutwardly counter to the action of the pistons of hydraulic systems 8,by pivotting of arms '7about fixed pivot axes 9. On the shaft of drivemotor 10 connected to disc roll 1, there is arranged a tachometergenerator 11 whose output voltage is proportional to the actual speed ofdisc roll 1 and influences, through a control device 12, the nominalvalue of speed regulator 13 for drive motor 14 oflower conical roll 3.On the shaft of drive motor 14, a tachometer generator 15 is arranged,whose output voltage is proportional -to the actual speed of conicalroll -3 and whichmay cause a speed correction through speed regulator13.

Two sensors 16 with respective measuringtransformers 17 are designedasfeeler wheels engaging the outer circumference of the ring, and thesesensors sense av diameter or a chord of the ring perpendicular-tothecommon axial plane of radial rolls 1 and'2. The ring diameter-dependentoutput value of a controldevice 18 connected to measuringtransformers l7representsa second control quantity for-control device 12 forinfluencing the speed of drive motor 14 0f conical roll 3. Thus, thebasic matching of the two speeds, asafunction of the actual speed ofdiscroll l'and ofthe relative position between ring 5 and conical rolls3, is made feasible.

If ring 5 leaves its symmetrical centered position by migrating, for.example upwardly in FIG. 1, because, in the pair of radial rolls 3, acontact point shift increasing the circumferential speed of the ring atan unchanged actual speed of disc roll 1, has occurred, then uppersensor 16 is deflected outwardly while lower sensor 16 follows the ringcircumference inwardly. Control device 18 then generates, from thesignals of the two measuring transformers 17, a difference signal which,through control device 12, so influences the nominal value for speedregulator l3 thatthe speed of lower driven conical roll 3 is increasedby an adequate amount and thus the ring is brought back to its centralpositiomControl device 12 includes an electrical holding member so thatthe disappearance of the difference voltage of control device 18,connected with the return of the ring to its centered position, againcauses a change of speed of the conical rolls. Only after a renewedmigration of the ring upwardly, or in the opposite direction downwardly,has occurred, is the output of control device 12 again influenced by adifference signal of control device 18 building up, and the speed ofdrive motor 14 of conical roll 3 is corrected accordingly.

In another embodiment of the invention, the centering wheels6 aredesigned as sensors so that-sensors 16 of the arrangement of FIG. 1becomes superfluous. As shown in FIGS. 2 and 3, the suspensions 19 ofcentering wheels 6 are pivotable about respective pivot axes .21 ofpivot arms 7 normal to centering wheel axes20. This pivoting is opposedby spring members 22, whose displacement constitutes and input value.for the respective measuring transformer 17 of the regulating device.The spring force of members 22 can be relatively small so that, as thering grows or expands radially in its centered position, eachsuspensionilflapplies against the lateralwall of the pivot arm 7 towardcentering wheel 6, and the contact pressure of the. centering wheels isdetermined by the hydraulic systems 8 of FIG. 1. If the ring migratesunilaterally upwardly, as viewed in FIG. 1, then the uppercenteringwheel 6 remainsin its normal position supported against thewallof pivot arm 7, while the lower centering wheel 6 pivots outwardly. As aresult, difference signalsare available atmeasuring transformers 17, andtheseare .used for the correction of the speed of one roll drive throughthe regulating device .in the manner already described in connectionwith FIG. 1. For. axial rolls fixed in the longitudinal direction of therolling mill, scanning of the instantaneous ring diameter is dispensedwith. Due .to :the increasein ring diameter, the ring migrates outwardlybetween the conical rolls 3, with the result that, starting from theinitial basic matching of the speeds, the drive speed of the conicalrolls 3 must be continuously re- .ducedin aniadequate manner. For thiscontinuous speed reduction, there isagain used the unilateral migrationof ring 5.

In the ring rolling mill shown in FIG. 4, the basic matching of thespeed of the two roll drives again is effected in that the outputvoltage of the tachometer generator l1, proportional to the'actualperipheral speed of-disc roll 1, is'used with the aid of the speedregulating device 23,. not shown in detail,=for.the basic matching ofthe roll drives. The conical rolls 3 are guided,.for

longitudinal displacement, in a slidein the roll stand,

this being indicated only by the double arrow 24 in FIG. 4. Thislongitudinal displacement of conical rolls 3 occurs, in a manner knownper se and not illustrated in detail, by a setting member, for example,a hydraulic system 25 which is actuated by a control device, forexample, a follow-up regulator 26, so that conical rolls 3 shift in thedirection of the double arrow 24 in accordance with the respective ringdiameter. The guide value for the position regulating circle of theconical roll displacement may be the signal of a device not shown, butknown in itself, influenced by the ring diameter, such as afeeler wheelor the like or, alternatively, the deflection of the sensors 27mentioned hereinafter.

Through pivot arms 7 of centering wheels 6, there are actuated twosensors 27 with associated respective measuring transformers 28, whichpick up the position of the centering wheels 6. The two measuringtransformers 28 of this position measuring unit are branches of ameasuring bridge 29. With the pivot arms 7 of centering wheels 6, inthis case acting as measuring sensors, there are engaged respectivehydraulic systems 30 with adjustable throttles 31. At a diameterincrease in the symmetrical ring position, sensors 27 provide identicalcontrol signals, so that measuring bridge 29 remains tuned and the twothrottles 31, controlled by the voltage in a neutral branch of measuringbridge 29, maintain the coincident state. Both throttles 31 are open toa large degree, so that the contact pressure of centering wheels 6 atring is accordingly low.

If the ring migrates out of the symmetrical position unilaterally, thensensors 27 cause a detuning of measuring bridge 29 proportional to themigration as to direction and magnitude. The voltage in the neutralbranch of measuring bridge 29 is used for controlling throttles 31. Thepassage resistance of that throttle 31 associated with the centeringwheel 6 which receives an additional deflection by themigration of ring5 is increased. Thereby, the pressure of this centering wheel 6 againstthe ring is adequately increased and a corresponding force is exerted onthe ring. Above all, however, the voltage in the neutral branch .ofmeasuring bridge 29 is supplied, as an additional guide or controlvalue, to the followup regulator 26 for the displacement of conicalrolls 3 in the direction of double arrow 24. The signal from the neutralbranch of measuring bridge 29 is superimposed on the signal whicheffects displacement of the conical rolls 3 in dependence only on thering diameter. The signal resulting from the super-position is the totalguide value for the position control circuit of the conical rolldisplacement. In this way, the signal in the neutral branch of measuringbridge 29 effects a return of the ring to its central position, byvariation of the peripheral speed of the driven conical roll 3 counterto or codirectionally with the ring growth. It is thus readily possibleto bring the peripheral speed of ring 5 at the roll pairs 1, 2 and 3, 3into coincidence with one another within narrow limits so extensivelythat, during rolling, ring 5 migrates only slightly to either side, andthe danger of ring deformations is practically eliminated.

FIGS. 5 and 6 illustrate the mechanical structural de sign of a ringrolling mill shown diagrammatically in FIG. 4, the means, in accordancewith the invention,

'force axially of the ring.

edging stand 33. In mill frame 34, common to both stands, the kingpin35, with disc roll 1, is mounted fixedly and is driven by an electricmotor 37 through a transmission 36. Opposite disc roll 3 anddisplaceable relative to this disc roll, the mandrel roll 2, which isnot driven, is mounted in a hydraulic slide 38 which is adjustable. Atits upper end, mandrel 2 is supported by the hydraulically raisable andlowerable frame type bracket 39. The two centering wheels 6 arerotatable in pivot arms 7 which are swingable about pivot axes 9, sothat centering wheels 6 can be applied against the ring to be rolled,which has not been shown in FIGS. 5 and 6. Edging stand 33 is arrangedfor horizontal displacement in slideways along frame 34, with suchdisplacement being effected by means of a double-acting hydraulic system25. In the power part of edging stand 33, lower conical roll 3 isfixedly mounted and is driven by an electric motor 41 through a fixedtransmission 40. The transmission and motor are so designed that thespeed of lower conicalroll 3 can be regulated so that the peripheralspeed of this conical roll can be adapted continuously to the rollingspeed of the disc roll 1 over the entire length of its conical surface.The upper conical roll 3 is mounted freely rotatable in a slide 42,which can be positioned in the axial direction of the workpiece ring tobe rolled, through a worm gear 44, driven by a motor 43, and a wormdrive 45. Additionally, slide 42 can be also lowered hydraulically,which has not been shown, to exert a vertical rolling The ring rollingmill of FIG. 1 is designed, in its mechanical construction,substantially the same way as that shown in FIGS. 5 and 6, withdifferences in certain parts.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. In a ring rolling mill including a pair of radial rolls acting on aworkpiece ring by engaging radially opposite peripheries of the ring,and a pair of axial rolls, which are preferably truncated conical rolls,acting axially on the ring by engaging axially opposite end surfacesthereof, the two rolls of each pair being adjustable relatively to eachother and at least one roll of each pair being driven, the improvementcomprising, in combination, respective adjustable speed driving meansfor each pair; means operable to adjust one driving means to apreselected nominal peripheral speed of the associated driven roll;first control means operable to adjust the other driving means to setthe peripheral speed of the driven roll associated with said otherdriving means in accordance with the peripheral speed of the roll drivenby said one driving means; sensor means operable to detect powertransmission, through the ring, between said driving means; and secondcontrol means operable, responsive to detection of such powertransmission by said sensor means, to restore the peripheral speeds ofsaid driven rolls into such accordance.

2. In a ring rolling mill, the improvement claimed in claim 1, in whichsaid sensor means comprises two sensors determining the position of twocircumferential points of the ring at opposite ends of a line extendingacross the ring perpendicularly to the common axial plane of said tworadial rolls.

3. In a ring rolling mill, the improvement claimed in claim 2, in whichsaid two sensor means are two feeler wheels engaging the outer surfaceof the ring.

4. In a ring rolling mill, the improvement claimed in claim 1, includingtwo centering wheels arranged mirror-symmetrically to the common axialplane of said two radial rolls and engaging the outer periphery of thering; at least one centering wheel constituting a sensor sensing thedisplacement force of the ring exerted thereon.

5. In a ring rolling mill, the improvement claimed in claim 4, in whichboth centering wheels are designed as sensors sensing the displacementforce of the ring exerted on the centering wheels.

6. In a ring rolling mill, the improvement claimed in claim 5, includinga respective suspension rotatably mounting each centering wheel; meansmounting each suspension for swinging about a pivot axis spaced from theaxis of the associated centering wheel; a spring biased member engagingeach suspension and biasing the suspension to rotate about its pivotaxis in a direction to maintain the associated centering wheel inengagement with the periphery of the ring; and a respective measuringtransformer associated with each centering wheel and forming part ofsaid second control means; the displacement of each spring biased memberproviding the input value for the associated measuring transformer.

7. In a ring rolling mill, the improvement claimed in claim 6, in whicheach said pivot axis extends perpendicularly to the axis of theassociated centering wheel.

8. In a ring rolling mill, the improvement claimed in claim 6, in whicheach pivot axis extends parallel to the axis of the associated centeringwheel.

9. In a ring rolling mill, the improvement claimed in claim 5, includinga respective switch element operatively associated with each centeringwheel; and a control device connected to said switch elements; saidswitch elements producing a signal in said control device responsive tounsymmetrical actuation of said switch elements.

10. In a ring rolling mill, the improvement claimed in claim 9, in whicheach switch element is a pressure switch actuated upon contact of theassociated centering wheel with the ring.

11. In a ring rolling mill, the improvement claimed in claim 1,including a single centering wheel engaging the outerperiphery of thering and positioned at that side of the ring rolling mill from which thering enters between the rolls of said pair of radial rolls.

12. In a ring rolling mill, the improvement claimed in claim 1, in whicheach driving means includes a respective electrical motor; and arespective measuring device operatively associated with each electricmotor and detecting the effective electric power drawn by the associatedmotor.

13. In a ring rolling mill, the improvement claimed in claim 1, inwhicheach driving means includes a respective electric motor; arespective measuring device operable to detect the effective electricpower drawn by each motor; and a respective measuring device at eachpair of rolls operable to sense the rolling force thereof.

14. In a ring rolling mill, the improvement claimed in claim 1, in whicheach driving means includes a respective electric motor; said secondcontrol means including a setting member whose setting value influencesthe speed of the drive motor of one pair of rolls.

15. In a ring rolling mill, the improvement claimed in claim 1, in whichsaid second control means includes a setting member operable to effectaxial displacement of said conical axial rolls relative to the ring.

16. In a ring rolling mill, the improvement claimed in claim 1, in whichsaid second control means comprises at least one setting memberinfluencing the rolling force exerted on the ring by at least one ofsaid pairs of rolls.

17. In a ring rolling mill, the improvement claimed in claim 1, in whichsaid second control means comprises two setting members each influencingthe rolling force exerted on the ring by a respective one of said pairsof rolls.

1. In a ring rolling milL including a pair of radial rolls acting on aworkpiece ring by engaging radially opposite peripheries of the ring,and a pair of axial rolls, which are preferably truncated conical rolls,acting axially on the ring by engaging axially opposite end surfacesthereof, the two rolls of each pair being adjustable relatively to eachother and at least one roll of each pair being driven, the improvementcomprising, in combination, respective adjustable speed driving meansfor each pair; means operable to adjust one driving means to apreselected nominal peripheral speed of the associated driven roll;first control means operable to adjust the other driving means to setthe peripheral speed of the driven roll associated with said otherdriving means in accordance with the peripheral speed of the roll drivenby said one driving means; sensor means operable to detect powertransmission, through the ring, between said driving means; and secondcontrol means operable, responsive to detection of such powertransmission by said sensor means, to restore the peripheral speeds ofsaid driven rolls into such accordance.
 2. In a ring rolling mill, theimprovement claimed in claim 1, in which said sensor means comprises twosensors determining the position of two circumferential points of thering at opposite ends of a line extending across the ringperpendicularly to the common axial plane of said two radial rolls. 3.In a ring rolling mill, the improvement claimed in claim 2, in whichsaid two sensor means are two feeler wheels engaging the outer surfaceof the ring.
 4. In a ring rolling mill, the improvement claimed in claim1, including two centering wheels arranged mirror-symmetrically to thecommon axial plane of said two radial rolls and engaging the outerperiphery of the ring; at least one centering wheel constituting asensor sensing the displacement force of the ring exerted thereon.
 5. Ina ring rolling mill, the improvement claimed in claim 4, in which bothcentering wheels are designed as sensors sensing the displacement forceof the ring exerted on the centering wheels.
 6. In a ring rolling mill,the improvement claimed in claim 5, including a respective suspensionrotatably mounting each centering wheel; means mounting each suspensionfor swinging about a pivot axis spaced from the axis of the associatedcentering wheel; a spring biased member engaging each suspension andbiasing the suspension to rotate about its pivot axis in a direction tomaintain the associated centering wheel in engagement with the peripheryof the ring; and a respective measuring transformer associated with eachcentering wheel and forming part of said second control means; thedisplacement of each spring biased member providing the input value forthe associated measuring transformer.
 7. In a ring rolling mill, theimprovement claimed in claim 6, in which each said pivot axis extendsperpendicularly to the axis of the associated centering wheel.
 8. In aring rolling mill, the improvement claimed in claim 6, in which eachpivot axis extends parallel to the axis of the associated centeringwheel.
 9. In a ring rolling mill, the improvement claimed in claim 5,including a respective switch element operatively associated with eachcentering wheel; and a control device connected to said switch elements;said switch elements producing a signal in said control deviceresponsive to unsymmetrical actuation of said switch elements.
 10. In aring rolling mill, the improvement claimed in claim 9, in which eachswitch element is a pressure switch actuated upon contact of theassociated centering wheel with the ring.
 11. In a ring rolling mill,the improvement claimed in claim 1, including a single centering wheelengaging the outer periphery of the ring and positioned at that side ofthe ring rolling mill from which the ring enters between the rolls ofsaid pair of radial rolls.
 12. In a ring rolling mill, the improvementclaimed in claim 1, in which each driving means includes a resPectiveelectrical motor; and a respective measuring device operativelyassociated with each electric motor and detecting the effective electricpower drawn by the associated motor.
 13. In a ring rolling mill, theimprovement claimed in claim 1, in which each driving means includes arespective electric motor; a respective measuring device operable todetect the effective electric power drawn by each motor; and arespective measuring device at each pair of rolls operable to sense therolling force thereof.
 14. In a ring rolling mill, the improvementclaimed in claim 1, in which each driving means includes a respectiveelectric motor; said second control means including a setting memberwhose setting value influences the speed of the drive motor of one pairof rolls.
 15. In a ring rolling mill, the improvement claimed in claim1, in which said second control means includes a setting member operableto effect axial displacement of said conical axial rolls relative to thering.
 16. In a ring rolling mill, the improvement claimed in claim 1, inwhich said second control means comprises at least one setting memberinfluencing the rolling force exerted on the ring by at least one ofsaid pairs of rolls.
 17. In a ring rolling mill, the improvement claimedin claim 1, in which said second control means comprises two settingmembers each influencing the rolling force exerted on the ring by arespective one of said pairs of rolls.